Hydraulic control mechanism



y 1949- G. G. DAVIS 2,475,313

HYDRAULIC CONTROL MECHANISM Filed June 28, 1943 Fi 9:1 72 46 ga a y 7w/amg I Inventov: k Glenn G. Daws, Q 1' L4 His Attorney.

Patented July 5, 1949 RAULIC CONTROL MECHANISM Glenn G. Davis,Schenectady, N. Y., asslgnor to General Electric Company, a corporationof New 1 York Application June 28, 1943, Serial No. 492,522

3 Claims. 7 l

The present invention relates to hydraulic control mechanisms of thetype in which two elements of a device, such as the casing and the Inservomotors the movement of the piston or I plunger is efiected bychange of pressure in the pressure chamber of the servomotor and thischange of pressure ordinarily is controlled by a pilot valve or likecontrol member. Any change in pressure in the pressure chamber of theservomotor creates a force, positive or negative, which tends to movethe piston. If the piston is already moving, a smaller force is requiredto afiect such movement than when the piston is at rest because in thelatter case the force must overcome the friction of rest of the pistonwhich is considerably higher than the friction of movement.

Whenever great accuracy is required of hydraulic control mechanisms itbecomes desirable to reduce the friction of rest to a minimum or toeliminate it entirely.

The general object of my invention is to provide an improvedconstruction and arrangement of hydraulic control mechanisms of the kindabove specified in which the friction of rest of a hydraulic device,especially of the piston of a hydraulic motor, is reduced orsubstantially eliminated. This is accomplished in accordance with myinvention by a hydraulic control mechanism which includes hydraulicmeans for vibra ing the piston or like element of a hydraulic motor orlike device. These means in a preferred embodiment consist of anadjustable flow control mechanism whereby the frequency of vibration ofthe element to be vibrated may be varied and maintained constant. Thevibrating means preferably has an auxiliary motor with a chamberconnected to the pressure chamber of the hydraulic motor to be vibratedand means for reciprocating the piston of the auxiliary motor to effecta continuous alternate increase and decrease of pressure in theauxiliary hydraulic motor, more particularly in the pressure chambertherein and accordingly in the pressure chamber of the main hydraulicmotor.

For abetter understanding of what I believe to be novel and myinvention, attention is directed to the following description and theclaims appended thereto in connection with the accompanying drawing.

In the drawing Fig. 1 illustrates a diagrammatic, perspective view,partly in section, of a hydraulic control mechanism embodying my in- 2vention: Fig. 2 is a perspective view of a detail of Fig. 1; Fig. 3 is asection along line 3--3 of Fig. 1; and Fig. 4 is a section along line4-4 of Fig. 3.

The arrangement shown in the drawing comprises a hydraulic. device inthe form of a hydraulic motor or se'rvomotor having a casing ill with acylindrical bore and a piston ll secured to a stem l2 slidably disposedin the cylindrical bore and forming therewith two pressure chambers l3,it on opposite sides of the piston H. The piston stem projects slidablythrough the end walls of the casing. 'The supply of fluid under pressureto the pressure chambers l3, it and the discharge of fluid therefrom arecontrolled by a control member or pilot valve l5 which has a casingunited with the casing ill and a cylindrical bore with a movable valvemember therein. This valve member has a stem l8 and valve heads [1, I8secured thereto and associated with two channels or ports I9, 20leadingv to the chambers l3, M. A third channel or port 2| is formed inthe casing between the valve heads I I, I8 and connected to a conduit 22for conducting fluid under pressure from a source, not shown, to thepilot valve l5.

In the position shown, the valve heads IT, it are in their normalposition in which they cover the ports i9, 20. Upon movement of thepilot valve stem 56 to the left, fluid under pressure may be conductedfrom the conduit 22 through the pilot valve and the port 19 to thepressure chamber it and at the same time fluid under pressure may bedischarged from the pressure chamber it through the port 20 and therighthandopen end of the pilot valve casing. During such operation thepiston H of the hydraulic motor with its stem i2 are forced towards theright and this movement continues until the pilot valve heads H, H! arerestored to their normal position in alignment with the ports i9, 20respectively.

Upon movement of the pilot valve stem it towards the right, fluid underpressure may be conducted from the conduit 22 to the chamber it whilefluid under pressure is discharged from the chamber l3 through thechannel l9 and the left-hand open end of the pilot valve casing.

In order to render the hydraulic mechanism sensitive to slight changesof fluid pressure in the chambers l3, ll means are provided for con- 3device, in the present example between the piston ll and the stem l2,and the casing ID. This means comprises auxiliary hydraulic motor means,in the present instance an auxiliary hydraulic motor 23, having a casing24 and a movable member 25 disposed in the casing 24 and formingtherewith two chambers 26 and 21 connected by channel members 28 and 29respectively to the pressure chambers |3, M respectively of thehydraulic motor. The movable member 25 has a stem 30 with two spacedpistons 3| and 32 attached to the stem 30 and slidably disposed within acylindrical bore of the casing 24. The aforementioned chamber 26 isdefined by said bore between one end of the casing 24 and the piston 3|while the chamber 21 is formed by said cylindrical bore between theother end of the casing 24 and the piston 32. The chambers 26 and 21communicate continuously with the pressure chambers l3, l4 and duringoperation therefore the chambers 26, 21 are continuously filled with oilor like operating fluid under pressure. The mechanism includes means forcontinuously vibrating or reciprocating the movable member 25 of theauxiliary motor 23. During such reciprocation the stem 30 is alternatelymoved to the right and to the left. Upon movement to the right thechamber 26 is enlarged and the chamber 21 is reduced. Thus, operatingmedium is forced from the chamber 21 into the pressure chamber l4 andsimultaneously operating medium is displaced from the pressure chamberl3 into the chamber 26. The opposite action takes place upon movement ofthe member 25 towards the left during which operating medium is forcedfrom the chamber 26 into the pressure chamber l3 and simultaneouslyoperating medium is displaced from the pressure chamber l4 into thechamber 21. Hence, reciprocation or vibration of the member 25 of theauxiliary motor causes reciprocation or vibration of the movable member|l, I2 of the main hydraulic motor. As the piston ll moves towards theright the pistons 3|, 32 move towards the left, that is, in the presentexample the two elements vibrate at the same frequency with a phaserelation of 180 degrees.

In order to effect vibratory or reciprocatory movement of the member 25,two pressure chambers 34 and 35 are formed adjacent the pistons 3|, 32respectively. These chambers are separated by a stationary wall 36between the pistons 3|, 32 fixed to the casing 24 by a key 31. Fluid maybe supplied to and discharged from the chambers 34, 35 by means ofchannel members 38 and 39 respectively. The mechanism includes means forcontrolling the supply and discharge of fluid under pressure to thechambers 34, 35 arranged alternately to effect supply of fluid to onechamber and discharge of fluid to the other, and vice versa. This meansincludes a rotary valve 40 together with another auxiliary hydraulicmotor 4|. As will be more fully described hereinafter, the auxiliarymotors 23 and 4| cause continuous rotation of the rotary valve 40whereby fluid is alternately supplied and discharged from the respectivepressure chambers of said motors and stalling of the rotary valve in thedead-center position of one of the motors is eliminated.

More specifically, the rotary valve 46 has a movable member producedfrom a cylindrical body forming spaced shaft portions 42 and 43supported on ball-bearings 44 and 45 respectively, held in a casing orstationary member 46. The movable valve member has two spaced, segment lcylinder portions 41, 43 which are angularly displaced by 180 degreesand connected by a flat portion 49. The portion 41 faces and is spacedfrom the shaft portion 42 and the portion 46 faces and is spaced fromthe shaft portion 43 (Figs. 2, 4).

The valve member is located within a cylindrical chamber 50 in thecasing 46. The casing has a plurality of ports cooperatively associatedwith the rotatable valve member. One port 5| connected to a supplyconduit 52 conducts operating fluid to'the annular inlet space formedbetween the bearing portion 42 and the segmental cylinder portion 41.Four circumferentially, uniformly spaced ports 53, 64, and 56 are formedin the casing 46 around the flat portion 49 of the rotatable valvemember. The ports 53 and 55 are spaced 180 degrees and connected to theaforementioned channel members 38, 39 respectively. .The other ports 54and 56 are likewise spaced 180 angular degrees and connected to channelmembers 51 and 58 respectively.

The channel members 51, 56 serve to control the supply of fluid to andthe discharge of operating fluid from the second auxiliary motor 4|. Thelatter has a casing 59 forming a cylindrical bore and a piston 50movably disposed therein and connected to a stem 6| projecting throughopposite ends of the casing. The piston and the spectively.

As pointed out above, the pistons of the two auxiliary hydraulic motors23, 4| are connected to drive the rotary valve 40. This is accomplishedby a crank shaft connection between the rotary valve 46 and the pistonstems 30, 6|. In the present example the shaft portion 43 of the rotaryvalve is provided with an extension 64 adiustably connected to a crankarm 65. The arm 65 is in the form of a block with a dovetailed slot forreceiving a dovetailed square portion 66 of the driven shaft 64. Twoscrews 61 through opposite wall portions of the crank arm and onopposite sides of the portion 66 bias these wall portions into firmcontact with the portion 66 of the driven shaft 64. When it is desiredto adjust the crank arm on the driven shaft 64 the screws 61 areloosened whereupon the crank arm may be slid relative to the portion 66.

A crank pin 68 is secured to'the crank arm 65. The crank pin 66 isengaged by two cross heads 69, 19 secured to the ends of the stems 36and 6| respectively. The cross heads in the present example are in theform of oval-shaped members each having a slot 1| through which thecrank pin 68 passes. The extensions of the stems 30 and 6| fastened tothe cross heads 69, 10 constitute connecting rods for connecting saidcross heads to the pistons 01' the auxiliary hydraulic motors 23 and 4|respectively.

In the position shown, oil or other operating fluid under pressure isconducted from the supply conduit 52 to the inlet space between theshaft portion 42 and the segmental cylinder portion 41 and from thisspace oil may flow along the' lower side of the flat portion 49 into theport 53 and through the channel member 36 to the pressure chamber 34 ofthe auxiliary motor 23. At the same time, oil may be discharged from theother pressure chamber 35 of this motor through the channel member 39and the port 55 of the rotary valve into the outlet space 12 formed tothe right of the segmental cylinder portion 41 and above the flatportion 49 (Fig. 4). The space 12 constitutes a drain chamber, fluidbeing discharged therefrom axially through the bearing 45 into areservoir, not shown. This fluid acts as a lubricant for the bearing 45.The other bearing 44 is lubricated by fluid leaking from the inlet spacealong the shaft portion 42. Thus, in the position shown, fluid underpressure is discharged through the port 53 to one pressure chamber ofthe motor 23 and returned from the other pressure chamber of said motorthrough the port 55. The two ports 54, 5B of the rotary valve member aresubstantially covered by the flat portion 49 of the valve member. Thesupply of fluid under pressure through the chamber 34, as pointed outabove, causes movement of the valve member 25 towards the left,resulting in rotation of the crank pin 68 and rotation of the rotatablevalve member. In the position shown in Fig. 1 the piston 60 and thecrank pin 68 are in their upper end positions. It would not be desirablein this position to supply operating fluid under pressure to the chamber53 because downward movement of the piston 60 effected by such supplycould not be usefully transmitted to the crank pin. Therefore themechanism is arranged to produce a delay between the downward movementof the piston 60 and the rotary movementof the crank pin 68 in orderflrst to rotate the crank pin 68 a certain angular degree away from itsupper end position before downward force is supplied thereto by actionof the piston 50. This is accomplished by offsetting the flat portion orport-controlling portion 49 of the rotary valve relative to the ports 53to 5-5. As shown in Fig. 3, in the position indicated the flat portion49 in the horizontal position is not in alignment with the ports 51, 59but is displaced about 15 angular degrees with respect to said ports.Hence, while the piston 69 is in its top upper end position bothchambers GI and 63 are connected to the discharge space 12 and thissimultaneous connection continues during approximately 15 degreesangular movementof the rotary valve member. During such movement thecrank pin 68 is moved away from its upper end position. Upon terminationof this delaying action the port 56 is uncovered so that fluid underpressure may be supplied through the port 56 into the chamber 53 of theauxiliary motor 4| and at the same time fluid may be discharged from thechamber 62 of said motor through the channel member 51, the port 54,into the drain space 12. This causes downward movement of the piston 60and through the connection of the latter to the crank pin 58 rotarymovement of the valve 40. Upon further rotary movement, ports 53 and 55are disconnected or covered by thefiat portion 49. While this takesplace the rotation of the valve 49 is effected solely by the auxiliarymotor 4i. Upon further rotation the rotatable valve member comes into aposition opposite that shown. In this case the port 55 is connected tothe supply conduit 52 and the port 53 is connected to the drain space ofthe valve, thus causing movement of the motor 24 in opposite direction.Upon further movement of the valve member the port 54 is connected tothe supply conduit 52 and the port 56 is connected to the drain chamber,causing upward movement of the second auxiliary motor 4|.

Thus, the two motors 23 and M together with the rotary valve cooperateto eifect continuous rotation of the valve 40 and vibratory axialmovement of the member 25 of the main motor 23. In order to maintainthis vibratory move ment at constant frequency and also to permitvariation of the frequency a flow control valve i3 is connected to thesupply conduit 52.

The flow control valve or constant flow valve 13 has a casing 14 forminga cylindrical valve chamber with an inlet connected to a conduit 15 forreceiving oil under pressure and an out: let port 18 connected to theaforementioned supply conduit 52. The flow through the valve iscontrolled by a movable valve member 11 which has a restriction 18 and alateral port 19 cooperatively associated with the outlet port I5.

The flow from the-port 19 to the port 15 depends upon the overlapbetween the two ports. The valve member 11 is biased towards the left bya spring hearing against the valve member H and against an adjustablespring plate 8|. During operation the pressure of the fluid passingthrough the orifice or restriction I8 is reduced. The valve member 11 isforced towards the right by the pressure exerted on the lefthand end ofthe valve member and this force is balanced by the force of the spring80 and the fluid pressure set up on the right-hand end of the valvemember 11. An increase in flow causes an increased pressure drop throughthe orifice 18 whereby the force exerted on the left-hand end of thevalve member H increases relative to the force on the right-hand end ofthe valve member 11, causing movement of the valve member towards theright and accordingly an increased overlap between the ports I9 and 11,thus reducing the flow therethrough or, from another viewpoint,preventing an increase in flow therethrough, thus maintaining the flowto the supply 'pipe 52 substantially constant and independent ofvariations in pressure in the inlet conduit 15. With constant flowthrough the supply conduit 52 the frequency of vibration of allhydraulic motors remains constant. This frequency of vibration may bevaried by adjustment of the spring plate 8| of the flow control valveI3.

. Having described the method of operation of my invention, togetherwith the apparatus which I now consider to represent the. bestembodiment thereof, I desire to have it understood that the apparatusshown is only illustrative and that the invention may be carried out byother means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is,

1. In a hydraulic control system the combination comprising a main servomotor having a servo cylinder and a piston movable in said cylinder, acontrol valve for selectively admitting fluid under pressure to eitherside of said piston to control movement of said servo motor, means forcausing a continuous vibratory movement of said piston to reduce staticfriction and thereby render said piston more sensitive to movement ofsaid control valve, said means comprising an auxiliary hydraulic motor,said auxiliary motor comprising first and second cylinders, piston meanscomprising first and second pistons cooperating respectively with andadapted to reciprocate in said first and second cylinders, valve meansoperated by said piston means for controlling the flow of hydraulicfluid to said auxiliary motorto reciprocate said piston means, conduitmeans connecting said valve means to one end only of said first andsecond cylinders, and conduit means connecting the other ends of saidfirst and second cylinders and opposite ends of said main servo motorcylinder whereby pulsations in fiuid pressure produced by operation 01.said auxiliary hydraulic motor are transmitted to said main servo motorto cause a vibratory movement of said piston oi. said motor.

2. In a hydraulic control system, a main hydraulic motor having movableand stationary members, one of said members defining a pressure chamberinto which hydraulic fluid is introduced at opposite ends of saidpressure chamber to cause movement of said movable member of said motor,means for causing a vibratory movement of said movable member comprisingan auxiliary hydraulic motor having first and second pistons operated bya common power means and reciprocating in first and second cylindersthereby defining a pair of chambers in opposed relation in each cylinderthe volumes of which are changed by reciprocation of said pistons, andfluid conduit means interconnecting two of said chambers in opposedrelation with said opposite ends of said main servo motor pressurechamber.

3. Means for causing a vibratory movement 0! a piston of a hydraulicservo motor, said motor having a pressure chamber into which hydraulicfiuid is introduced to control movement of said piston of said servomotor, said means comprising an auxiliary hydraulic motor having twocylinders and pistons reciprocating in said cylinders, said cylindersand pistons defining cham- REFERENCES CITED The following referenlcesare of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 409,457 Dennis Aug. 20, 18691,411,991 Doran Apr. 4, 1922 1,511,425 Rouka Oct. 14, 1924 1,967,851Wilson July 24, 1934 2,179,179 Rischel NOV. 7, 1939 2,194,914 Ruch Mar.26, 1940 2,246,074 Joy June 17, 1941 2,270,585 Gartner Jan. 20, 19422,350,117 Kline May 30, 1944 2,368,628 Bates Feb. 6, 1945 2,405,759Schnell Aug. 13, 1946

